Onco-developmental antigens are being studied in normal and leukemic chickens. Objectives are to determine the presence and function of the onco-developmental antigens during chicken development, cellular differentiation and malignancy. Onco-developmental antigens will be used to test the developmental blockage of cellular differentiation theory as one: possible cause of malignancy. Studies on genic regulation of the onco-developmental antigens during avian development will involve analyses of the developing chicken as well as related avian species, genetically produced interspecific hybrids and human-made interspecific chimeras. The hypothesis that onco-developmental antigens may serve as viral receptors will be examined. The enhancing and/or suppressive effect of chicken alpha-fetoprotein isolated from 14-day chicken embryo sera on the immune response system of adult chickens will be investigated.